This is a competitive revision application for R01 AR048328 in response to NIH Notice NOT-OD-09- 058: "NIH Announces the Availability of Recovery Act Funds for Competitive Revision Applications". Osteogenesis Imperfecta (OI) is a genetic disease caused by mutations in the type I collagen genes COL1A1 or COL1A2 that can result in major skeletal abnormalities, fractures, and premature death. We showed previously that gene targeting vectors based on adeno-associated virus (AAV) can efficiently disrupt mutant COL1A1 and COL1A2 genes in mesenchymal stem cells (MSCs) from individuals with OI, and that these MSCs then produced normal collagen and formed bone. In this R01, we received funding for three specific aims: to develop improved AAV vectors that target mutant collagen genes, to determine the effects of genetic polymorphisms on targeting, and to transplant MSCs and measure engraftment using a rabbit model. These Aims are intended to develop a therapeutic strategy consisting of isolation of a patient's MSCs, gene targeting to eliminate the mutant collagen gene, and transplantation of these autologous, targeted MSCs. While this remains a promising approach, its major shortcoming is the number of MSCs that can be obtained during ex vivo expansion. In this competitive revision application we propose to overcome this potential limitation by deriving induced pluripotent stem cells (iPSCs) from OI MSCs, which are immortal and capable of differentiating into MSCs and forming bone in vivo. We will derive iPSCs from OI MSCs, correct the collagen mutations in them by AAV-mediated gene targeting, and demonstrate these iPSCs can still form bone. PUBLIC HEALTH RELEVANCE: These experiments are meant to develop a new therapeutic paradigm, in which patient-specific pluripotent stem cells (iPSCs) are corrected by gene targeting and then returned to the patient. They will establish the feasibility of correcting genetic mutations in iPSCs and using these cells to generate bone, with major significance for the treatment of genetic diseases such as osteogenesis imperfecta.